Biodiesel refers to a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100, and meeting the requirements of ASTM D 6751. Currently, the most common method of Biodiesel production is trans-esterification of edible and non-edible vegetable oils, or sometimes animal fats. The trans-esterification reaction transforms triglycerides into fatty acid alkyl ester, in the presence of an alcohol, such as methanol or ethanol, and a catalyst, such as an alkali or acid, where glycerol is a by-product. Biodiesel has a comparable cetane rating and energy content to petro-diesel and hence is considered to be a perfect substitute to petro-diesel. It can either be used in pure from (100%) or is blended with petro-diesel is varying proportions. Soybean and Rapeseed are a common source of vegetable oils for biodiesel production. Such vegetable oils are in the form of triglycerides, which then need to be degraded to free-fatty acids and glycerol, where the fatty acids are esterified either chemically or enzymatically by the process known as ‘transesterification’. This poses an enormous strain on available arable land for production of both food-crops and fuel-crops, thereby exerting an undesirable pressure on food prices. Furthermore, since oil-seeds are a seasonal crop, once the crop is harvested and utilized, one has to wait until the next harvest is ready. Accordingly, their exits a need to overcome the food-OR-fuel dilemma, as well as a continuing need to shift global energy consumption from fossil fuels to environment-friendly biofuels. A further goal is to exploit energy sources such as cheap carbon sources which are by-products of established biodiesel Industry (Glycerol), as well as the most abundant non-edible sugar-sources available in nature, namely lignocellulose. The use of non-starch carbon sources such as cellulose, hemicelluloses, xylose, and lignin will not only favour the economics of bulk production of biodiesel, but will also reduce the strain on agricultural resources needed to satisfy society's need for food.
Although attempts have been made to manipulate microbial organisms biodiesel production, a principal barrier to success has been the development of robust, high-yielding microbes and processes for their production